Automatic sprinkler systems are some of the most widely used devices for fire protection. These systems have sprinklers that are activated once the ambient temperature in an environment, such as a room or building exceeds a predetermined value. Once activated, the sprinklers distribute fire-extinguishing fluid, preferably water, in the room or building. A sprinkler system is considered effective if it extinguishes or prevents growth of a fire. The effectiveness of a sprinkler is dependent upon the sprinkler consistently delivering an expected flow rate of fluid from its outlet for a given pressure at its inlet. The discharge coefficient or K-factor of a sprinkler allows for an approximation of flow rate to be expected from an outlet of a sprinkler based on the square root of the pressure of fluid fed into the inlet of the sprinkler. As used herein, the K-factor is defined as a constant representing the sprinkler discharge coefficient, that is quantified by the flow of fluid in gallons per minute (GPM) from the sprinkler outlet divided by the square root of the pressure of the flow of fluid fed into the inlet of the sprinkler passageway in pounds per square inch (PSI). The K-factor is expressed as GPM/(PSI)1/2 can provide for a rated or nominal K-factor or rated discharge coefficient of a sprinkler as a mean value over a K-factor range. For example, for a K-factor greater than 11, the following nominal K-factors (with the K-factor range shown in parenthesis) can be expressed as: (i) 14.0 (13.5-14.5) GPM/(PSI)1/2; (ii) 16.8 (16.0-17.6) GPM/(PSI)1/2; (iii) 19.6 (18.6-20.6) GPM/(PSI)1/2; (iv) 22.4 (21.3-23.5) GPM/(PSI)1/2; (v) 25.2 (23.9-26.5) GPM/(PSI)1/2; and (vi) 28.0 (26.6-29.4) GPM/(PSI)1/2; 33.6 (32.7-34.5) GPM/(PSI)1/2; 36.5 (34.9-38.1) GPM/(PSI)1/2 or higher.
The fluid supply for a sprinkler system may include, for example, an underground water main that enters the building to supply a vertical riser. At the top of a vertical riser, an array of pipes extends throughout the fire compartment in the building. In the piping distribution network atop the riser includes branch lines that carry the pressurized supply fluid to the sprinklers.
An automatic sprinkler may be configured for addressing a fire in a particular mode such as for example, control mode or suppression mode. Fire suppression is defined in the industry accepted standard, the National Fire Protection Association (NFPA) standard entitled, “NFPA 13: Standards for the Installation of Sprinkler Systems” (2010 ed.) (“NFPA 13”) and its updated edition NFPA 13 (2013 ed.), Section 3.3.10 as “[s]harply reducing the heat release rate of a fire and preventing its regrowth by means of direct and sufficient application of water through the fire plume to the burning fuel surface.” A sprinkler that provides for fire suppression is a suppression mode sprinkler. A suppression mode sprinkler can be “listed” as a sprinkler that has been tested, verified and published in a list by an industry accepted organization, such as for example, FM Global (“FM”) and Underwriters Laboratories (“UL”) as a sprinkler being suitable for the specified purpose of fire suppression.
Early Suppression Fast Response (ESFR) is defined under NFPA 13, Section 3.6.4.2 as a sprinkler having a thermal sensitivity, i.e., response time index (“RTI”) of 50 meter1/2second1/2 (“m1/2sec1/2”) or less and “listed” for its capability to provide fire suppression of specific high-challenge fire challenges. The “RTI” is a measure of thermal sensitivity and is related to the thermal inertia of a heat responsive element of a sprinkler. While ESFR sprinklers can be defined by the RTI of the sprinkler and its performance under the test standards, it should be understood that “suppression” mode sprinklers are not necessarily limited to ESFR sprinklers or sprinklers having an RTI of 50 or less. Accordingly, suppression mode sprinklers satisfying standardized test and/or other suppression criteria may have a thermally sensitive trigger having an RTI of ordinary or standard response sprinklers, i.e., RTI of 80 or greater.
According to the description in U.S. Pat. No. 5,829,532, when “fast response” was being investigated in the 1980's, “standard sprinklers” were found to have an RTI of more than 100 m1/2sec1/2 or more typically up to nearly 400 m1/2sec1/2; and for sprinklers that were found to thermally respond faster than standard sprinklers, the RTI was found to be less than 100 m1/2sec1/2. Currently under NFPA 13, Section 3.6.1, a “fast response” sprinkler is defined as a sprinkler having a thermal element with an RTI of 50 m1/2sec1/2 or less; and a “standard response” sprinkler is defined as a sprinkler having a thermal element with an RTI of 80 m1/2sec1/2 or more. Historically, a class of “special” faster operating sprinkler had been recognized having RTIs between 80 and 50 m1/2sec1/2. For one type of fast-response sprinkler, the early suppression fast response (“ESFR”) sprinkler, the thermal trigger has an RTI of 50 m1/2sec1/2 or less, more particularly 40 m1/2sec1/2 and even more particularly 19 to 36 m1/2sec1/2. It was once believed for fast-growing industrial fires of the type to be protected by ESFR sprinklers, that the RTI and the temperature rating together ensured adequate fast sprinkler response. Accordingly, some ESFR sprinklers include a trigger having an RTI of less than 40 m1/2sec1/2 and a temperature rating of 165° F. or 214° F. However, as described in U.S. Pat. No. 5,829,532 one embodiment of a sprinkler provided suppression of a high challenge fire with an trigger having an RTI of less than 100 m1/2sec1/2. Accordingly, as used herein, fast-response triggers can be characterized by RTIs of less than 100 m1/2sec1/2; 80 m1/2sec1/2 or less; 50 m1/2sec1/2 or less; 40 or less m1/2sec1/2 or ranging between 19 to 36 m1/2sec1/2.